1. Field of the Invention
The present invention relates to a control circuit of a power supply, a power supply and control method thereof.
2. Description of Related Art
Because reduction of the voltage of a power supply has been accelerated with progress of integration in integrated circuits (IC) in recent years, consumption of power has been reduced so as to achieve power saving. The threshold voltage of a MOS transistor loaded on an IC has been dropping with reduction of the voltage of the power supply in the IC of recent years. The reduction of the threshold voltage deteriorates the current interruption characteristic in a sub-threshold region, so that leak current sometimes flows out even in OFF state in which no voltage is applied between the gate and source of the MOS transistor. Thus, influences of the leak current cannot be neglected to achieve the power saving by reducing the consumption amount of power.
To suppress a flow of leak current in the MOS transistor, arts described in Japanese Unexamined Patent Publication H7-176624 and Japanese Unexamined Patent Publication H7-111314 have been known. In the integrated circuit described in the Japanese Unexamined Patent Publication H7-176624, when the PMOS transistor is off, a back gate voltage higher than when the PMOS transistor is on is applied to the back gate of the PMOS transistor and a back gate voltage lower than when the NMOS transistor is on is applied to the back gate of the NMOS transistor so as to raise the threshold voltage of each transistor, thereby suppressing the flow of leak current and reducing the consumption of power.
In the integrated circuit described in the Japanese Unexamined Patent Publication H7-111314, its back bias generating circuit applies a voltage higher than the voltage of the power supply to the N substrate of the PMOS transistor and applies a voltage lower than the grounding voltage to the P substrate of the NMOS transistor so as to raise the threshold voltage of each transistor and reduce the junction capacity, thereby suppressing the flow of the leak current and reducing the consumption amount of power.